This invention relates to substrate coatings containing energy absorbing, temperature stabilizing phase change materials and methods of manufacturing same. More particularly, this invention relates to fabric coatings containing microspheres of phase change material dispersed in a polymer binder and methods of manufacturing same.
Coatings are typically applied to fabrics to increase water resistance, water transport, insulative ability or heat storage properties of the fabrics. Recently, microencapsulated phase change materials have been described as a suitable component for fabric coatings when exceptional heat transfer and storage capabilities are desired. In particular, International Patent Application No. PCT/US93/05119 for xe2x80x9cFabric with Reversible Enhanced Thermal Propertiesxe2x80x9d to Colvin, et al., which is incorporated herein by reference, discloses that fabrics coated with a binder containing microcapsules filled with energy absorbing phase change material enables the fabric to exhibit extended or enhanced heat retention or storage properties.
Research has demonstrated that applying a binder containing microspheres of phase change materials with commercial coating equipment can be problematic. For example, use of solvent based gravure printing techniques in which a solvent system was employed to achieve uniform dispersion of the microspheres in a binder proved unsuccessful because the solvent systems damaged the microspheres.
Thermoplastic gravure printing techniques also proved unsatisfactory for use with microspheres of phase change material. When using higher temperature thermoplastic gravure printing techniques, sustained temperature of 325xc2x0 F. caused severe damage to the microspheres. Although lower temperature thermoplastic gravure printing techniques avoided significant damage to the microspheres, the resulting coating was found lacking in washability and durability. Moreover, lower temperature thermoplastic gravure printing techniques precluded addition of the desired amounts of the microspheres, allowing addition of microspheres of up to only about 20% by dry weight of the microsphere/binder material. This low percentage of phase change material in the coating makes the coating susceptible to undesirable heat transfer across the coating, especially in locations where phase change material is sparsely applied.
Attempts to encapsulate microspheres of phase change materials in a thermoplastic spray have also proved unsatisfactory. In particular, scattering microspheres into a stream of sprayed, fibrous thermoplastic material resulted in a binder matrix that did not fully encase the microspheres. The resulting binder/microsphere material was susceptible to loss of microspheres, which worked loose and were continually shedded from the fabric. In addition, the coating lacked uniformity of thickness and microsphere distribution.
Attempts were also made to utilize thermoplastic extrusion techniques to create a film of continuous web in which microspheres of phase change material were uniformly distributed. However, thermal breakdown of the microspheres resulted from the higher temperatures utilized. The extrusion screw employed with these techniques also physically damaged the microspheres.
Phase change materials in microencapsulated form are commonly supplied as a dry powder. This powder is difficult to wet and uniformly disperse in aqueous systems. Moreover, some microencapsulated phase change materials have an internal layer of modified gelatin which is hydrophilic and capable of absorbing its own weight in water. Not only does the hydrophilic quality of such microcapsules make more standard component proportions inapplicable, microcapsules which have absorbed water tend to swell and associate, increasing the viscosity of the coating system above acceptable limits. Although the precise behavior of microcapsules in the coating system which have absorbed water is uncertain, it is believed that such microcapsules agglomerate, reducing their dispersion throughout the binder of the coating system, which de-stabilizes the binder. This de-stabilization can increase over time. When latex binders are used with microencapsulated phase change material, de-stabilization of the latex binder can continue until the latex binder coagulates.
U.S. Pat. Nos. 5,254,380, 5,211,949, 5,282,994 and 5,106,520 for xe2x80x9cDry Powder Mixes Comprising Phase Change Materialsxe2x80x9d describe free flowing, conformable powder-like mixes of silica particles and a phase change material which the silica particles of between 7xc3x9710xe2x88x923 to 7xc3x9710xe2x88x922 microns are mixed with phase change material in a ratio of up to 80% by weight of phase change material. While these patents describe a matrix in which microspheres of phase change materials need not be separately encapsulated, they do not describe the use of dry powder mixes containing phase change materials in binder matrices for coating fabrics.
Research has further demonstrated that in applying a binder containing microspheres of phase change materials directly to a fabric, a significant amount of binder must be applied if a high content of microencapsulated phase change material is desired. For some commercial uses, however, a thick, exposed coating layer may be undesirable for the finished product.
This problem can be overcome in certain applications by insertion or lamination of the exposed coating between external sheets, substrates or fabrics of the finished product. Such constructions prevent the coating from contact with the end-user or exposure to view. The finished products necessarily contain additional layer(s) of substrate, whose function is, at least in part, to cover the otherwise exposed coating. In the case of a jacket lining or footwear insert, such a construction is not problematical. In other applications, however, it may be undesirable to have an additional covering layer which may needlessly add weight and/or bulk to the end product.
For certain other applications, it is desirable to use highly extensible fabrics. Typically, these fabrics have an ultimate elongation at break (UE) of more than 20%. Examples of extensible fabrics include knits, fabrics made from crimped or texturized yards, and fabrics made from rubber or polyurethane based yarns (such as Spandex(trademark), made by E.I. duPont de Nemours, Co.). Garments such as stockings, undergarments, sweaters, T-shirts, gloves, wet-suits, etc. must be extensible if they are to be put on easily and worn comfortably.
If a coating to be applied to an extensible fabric contains encapsulated phase change materials and has a UE much less than that of the fabric, the coating will prevent the coated fabric from stretching and making it stiff and unacceptable for use. On the other hand, if the modulus of elongation of the coating/phase change material is too high, it may make the coated fabric stiff or boardy and unsuitable for the end use.
The aforementioned problem may be solved by making a coating which is weak and has a very low UE. When such a weak coating is stretched, it breaks in many places. While this has the advantage of making the coating breathable, the product will exhibit a stiff hand until the coating is broken, after which the hand will vary from place to place on the fabric and the coating will be unsightly and may be unacceptable to consumers. In addition, the broken coating will be less resistant to wear and cleaning, pieces of the coating may break off or wear off. Finally, the portions of the stretched fabric which are no longer covered by coating will not have desired thermal properties, reducing the effectiveness of the phase change material.
It is well known that adding non-extensible particles, such as filler, reinforcements, or microencapsulated phase change materials to an elastomeric binder, reduces the UE of the composition and stiffens it. The amount of change depends principally upon the relative volumes of the filler and the elastomer, the amount of adhesion between the filler and the elastomer, and the dispersion of the filler in the elastomer. Moreover the effect of filler concentration on UE is non linear. As filler is increased, the UE falls off moderately until a concentration is reached where the UE is reduced drastically. The concentration at which the UE falls drastically depends upon the filler (as above) and upon the elastomer.
In general, it appears that coatings applied under tension to fabric may result in a coated product which does not exhibit the full stretch and recovery required for the most exacting applications. In addition, it has been found then that when binders containing a 40-50% phase change material content are applied by means of direct coating methods to stretch fabrics, the fabric tends to neck down before reaching the coating head and after being unrolled from the bolt upon which it is stored. The coating is then applied to the necked down fabric at the coating head, after which the coating is susceptible to cracking when the fabric is later stretched during manufacture or use. Even when the coating doesn""t crack, it may limit the natural stretchability of the fabric, as described above.
It is against this background that the significant improvements and advancement of the present invention have taken place in the field of fabric coatings containing energy absorbing, temperature stabilizing phase change materials and methods of manufacturing same.
It is the principal object of the present invention to provide an improved fabric coating composition containing phase change material of a density sufficient to effect or control heat and energy transfer across the coating and/or store heat in the coating.
It is another object of the present invention to provide a coating composition of the foregoing character which will maintain substantially all of the breathability, flexibility or other principal qualities of the fabric to which it is applied.
It is a further object of the present invention to provide coated fabrics having the aforementioned properties which are resistant to heat, pressure and chemicals encountered during the coating process.
It is a still further object of the present invention to provide coated fabrics having the aforementioned qualities which are durable, resistant to heat, moisture, solvents, laundering, and/or dry cleaning, without degradation to or loss of the phase change material.
It is still another object of the present invention to provide an improved method of applying coating compositions containing phase change materials and having the aforementioned qualities as coatings on fabrics by utilizing commercially available equipment.
It is yet another object of the present invention to provide an improved method of applying coatings containing phase change materials to fabrics without damage or degradation to the phase change materials.
It is still another object of the present invention to provide an improved method for evenly dispersing phase change material throughout a binder and maintaining an even distribution of the phase change material while coating a fabric with the binder and phase change material dispersion.
It is still another object of the present invention to develop a coating formulation and method suitable for application of a binder and phase change material composition to extensible fabrics.
It is a yet further object of the present invention to achieve the aforementioned objects which producing a coated fabric which is atheistically pleasing.
The present invention comprises coatings for fabrics and methods for manufacturing the same. A preferred coating includes wetted microspheres containing a phase change material dispersed throughout a polymer latex binder, and including a surfactant, a dispersant, an antifoam agent and a thickener. Preferred phase change materials include paraffinic hydrocarbons. To prepare a preferred coating composition of the present invention, microspheres containing phase change material are dispersed in an aqueous solution of a surfactant, a dispersant, and an antifoam agent mixture, followed by dispersion in a polymer mixture to form a coating composition. An alternative method of preparing the coating composition of the present invention includes dispersing microspheres containing phase change material in wet cake form in an aqueous solution of a surfactant, a dispersant, antifoam agent and polymer to form a coating composition. The coating composition of the present invention are then applied as a coating on a fabric.
In an alternative embodiment, a substrate is coated with an extensible binder containing microencapsulated phase change material to form an extensible, coated fabric. A preferred binder contains latex and a preferred substrate is an extensible fabric. The coated substrate is optionally flocked. When the coated product is an extensible fabric, transfer coating techniques are preferably employed.